1. Field of the Invention
The present invention relates to an apparatus of a Universal Serial Bus (USB) device to control power supply for the USB device, and in particular, to control power supply for a plurality of coupled USB devices.
2. Background of the Related Art
There are many bus standards for connecting an external peripheral device to a personal computer (PC). The USB, one of the bus standards, ensures high-speed serial data communication and convenient physical connection to a port. At this time, it is possible to connect 127 USB devices to a single USB port through a USB Hub, etc. Owing to such features, peripheral devices such as a mouse, a keyboard, a printer, a modem, a joystick and so on are adopting the USB interface USB i/F more and more.
The USB consists of four signal lines, two lines D+/D− for carrying data signals and two power lines +5V/GND. FIG. 1 shows a PC (host) and several USB devices 110 connected to the PC through a USB Hub 100 according to the related art. The USB Hub 100 is fed with necessary electric power by the PC through a USB or by an AC adapter converting an AC power to DC.
However, the related art USB hub has various disadvantages. The related art USB Hub 100 continues to supply electric power for the connected USB devices 110 as well as an internal circuitry 101 until it is commanded to turn off power for those devices. However, a connected USB device may be tuned off and power supplied is therefore wasted. Further, the related art USB Hub 100 continues to supply electric power for the connected USB devices 110 as well as an internal circuitry 101 until it is turned off, although a connected host USB has a failure. However, a connected USB device can not perform valid operations when data communication with a host is abnormal or fails. Therefore, while a connected host can not communicate, electric power supplied for a USB device is wasting.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.